Adjustable electrical instruments



Feb. 6, 1962 M. E. BOURNS ETAL ADJUSTABLE ELECTRICAL INSTRUMENTSOriginal Filed May 20, 1957 United States Patent 3,020,505 ADJUSTABLEELECTRICAL INSTRUMENTS Marian E. Bourns and Carl N. Boode, Riverside,and Edward D. OBrian, Anaheim, Calif.; said Boode and OBrian assignorsto Bourns, Inc., a corporation of California Original application May20, 1957, Ser. No. 660,247, now Patent No. 2,932,808, dated Apr. 12,1960. Divided and this application Apr. 8, 1960, Ser. No. 23,123

9 Claims. (Cl. 338-43) time a large number of such instruments utilize aresistance element and contact means resiliently engaging the resistanceelement so as to permit adjustment of the relative positions of thesetwo parts. In most cases instruments using both a resistance element andcontact means are formed in order to obtain a potential dividing action;

hence, they may be termed potentiometers even if they are manufacturedso as to be capable of other than manual adjustment. Frequently,however, such instruments are used in order to vary a resistance value;instruments of this category may be termed variable resistors.

Although a large number of attempts have been made to develop andmanufacture satisfactory composition and other resistance elements foruse in potentiometers and variable resistors, experience has proved thevalue of instruments of this category in which a wound resistanceelement is created by winding an appropriate Nichrome Wire or theequivalent upon a non-conductive carrier or mandrel. With this type ofconstruction the wire in effect extends along a helical path andresembles a common coil spring in configuration. With conventional wirewound variable resistors and potentiometers the contact means employedare mounted so that during adjustment the resistance element and/ or thecontact means employed are moved so that the contact means in effectjumps from one turn of the resistance wire to the next turn.

With this type of construction when the change in resistance between thecontact member and one end of the resistance element is plotted on agraph against the adjustment of the instrument itself a curve isobtained which tends to have a stair-step appearance. For manyapplications it is desired that this curve be of a smooth, continuouscategory in order to provide uniform readings. The term resolution isused in the industry so as to indicate the degree to which avcurve ofthis type tends toward smoothness. Thus, the operation of apotentiometer or a variable resistor having. a high degree of resolutionmay be graphically illustrated in this manner, and the curve obtainedwhile of a jumping or zig-zag category nevertheless tends to be of asmoother nature than an equivalent curve for a potentiometer or variableresistor having comparatively low resolution.

In order to provide electrical instruments such as potentiometers andvariable resistors having a high degree of resolution a number ofdiiferent expedients have been proposed. Usually the resolution ofpotentiometers is increased by forming elongated resistance elements outof comparatively fine wire. This type of solution to the problem isdisadvantageous inasmuch as fine wire tends to be relatively expensiveand somewhat difficult to hangreat or, in effect, infinite resolution.

A broad object of the present invention is to provide potentiometers andvariable resistors having extremely great or substantially infiniteresolution. A related object of the present invention is to provideinstruments of this category which may be manually actuated, or whichmay be actuated in accordance with the variables such as acceleration,pressure or the like. Another object of the present invention is toprovide new and improved potentiometers and variable resistors which maybe easily and inexpensively manufactured and which are extremelyreliable in use.

Because of the nature of this invention and because of the fact that agreat many difierent constructions fall ,Within the general scope of theinvention itself, and because of the fact that many of theseconstructions are in and of themselves considered to be of an inventivenature, it is not considered necessary to set forth in the initial partof this specification a detailed list of various objects and advantagesof each of the various constructions falling within the scope of thisinvention. Further, various other objects and advantages of theinvention will be fully apparent to those skilled in the art to whichthis invention pertains from an examination of the appended. claims andthe accompanying drawings in which:

FIG. 1 is a partial cross-sectional view of an acceleration responsivepotentiometer or accelerometer of the present invention; and 7 FIG. 2 isa detailed view of a contact member employed in the instrument shown inFIG. 1.

The accompanying drawings are not to be considered as limiting thepresent invention in any respect. Obviously a wide variety ofdifferently appearing instruments may be manufactured which utilize theessential features and principles of operation set forth in thisspecification and illustrated in the drawings. Whenever convenient forpurposes of illustration and explanation like numerals have been used todesignate like parts in various figures of the drawing.

As an aid to understanding the basic features of this present inventionit may be stated in essentially sumof which includes: an elongated,wound resistance element having an axis extending along its length;condie satisfactorily in many manufacturing operations. Also tact meansresiliently engaging substantially all points of this resistance elementin a plane perpendicular to the axis of the element; means for varyingthe relative positions of the resistance element and the contact meansso that the contact means at all times engages substantially'all pointsof, this resistance in a plane perpendicular to the axis of theresistance element itself. Within the broad'scope of this inventioninstruments are involved in which the resistance element itself may belocated on either the outside of an appropriate mandrel or be locatedwithin an internal cavity and in which the resistance element itself orthe contact means employed or both are capable of being moved so as tovary their relative positions.

The nature of the contact means employed with the present invention isconsidered to be important. Such contact means may comprise or include aresilient wire ring or a plurality of resilient fingers. Such fingersmay advantageously be manufactured so as to have diiferent resonantfrequencies by either varying their lengths or their weights. When thevarious resilient fingers employed in a contact member or a contactmeans of the present invention differ from one another in this manner,the contact means employed do not vibrate at the same frequency and,hence, various errors caused by vibration are substantially eliminated.

The use of contact means of the type broadly indicated in the precedingin conjunction with wound resistance elements has a number of practicalramifications. Frequently prior potentiometers and variable resistorshave been manufactured with comparatively long resistance elements so asto obtain satisfactory resolution. Because of the high degree ofresolution possible with electrical instruments constructed inaccordance with the teachings of this invention, instruments having verysatisfactory resolution for virtually any purpose can be manufacturedhaving relatively short resistance elements. These elements can besatisfactorily formed of comparatively high resistance wire so as tolessen the size required for an instrument of this invention below thatof comparable conventional instruments. The fact that such resistanceelements can be manufactured so as to be relatively short has the effectthat instruments falling within the scope of this invention may bedirectly connected to bellows, Bourdon tubes, etc., used in adjusting orvarying the relative positions of the contact means and the resistanceelements in units of this invention. Such elimination of conventionalmechanical linkages such as conventional multiplying linkages has theresult that the instruments of the present invention tend to berelatively simple to construct. Such elimination of parts is also veryadvantageous in overcoming friction and vibration errors such as areoften encountered with accelerometers or various types of pressureresponsive instruments.

The basic principle of this invention can also be applied to advantagewith accelerometers, as is evident from the disclosure container in theaforementioned Patent No. 2,932,808, the disclosure of which isincorporated herein by reference. In FIG. 1 of the drawing there isshown an accelerometer 336 having a housing 338 formed of anon-conductive material so as to have internal shoulders 340 locatedtherein. Within this instrument corrugated, spring-like metal diaphragms342 are held against these shoulders by means of non-conductive end caps344 which may be held in place by means of an adhesive ring 346. Each ofthese diaphragms 342 is provided with a centrally located aperture 348and these apertures 348 are connected together by means of a passage 350located so as to extend through the center of an elongated cylindricalweight or mass 352. Such a mass 352 may be conveniently formed of metaland may be attached to the diaphragms 342 by means of welding,soldering, or other equivalent techniques. Around the center of weight352 there is provided an external groove 354 which is adapted to carryan interior snap ring 356 formed as a part of a contact member 358 asindicated in FIG. 1 of the drawing. This contact member can beconveniently formed out of resilient metal so as to include a connectingradial section 360 and a resilient band 362 which resiliently bearsagainst a cylindrical resistance element 364 formed so as to besupported by and attached to the housing 338. Appropriate wire leads 366are connected to the ends of this resistance element 364 so as to extendto the exterior of the housing 338. Another similar lead 366 is attachedto one of the diaphragms 342 so as to also extend through the housing338.

It will be realized that as the accelerometer 336 is subjected toacceleration with the weight or mass 352 will be moved within thehousing 338 and that the passage 350 within this mass connecting what ineffect are chambers defined by each of the end caps 344 and each of thediaphragms 342 will act as an air damping passage to prevent unnecessaryor overly rapid movement of this weight. Obviously various types ofadjustable orifices or the like may be incorporated within theinstrument 336 so as to control the damping. During such movement of themass 352 the contact member 358 will be moved within this instrument soas to engage successive portions of the resistance element 364. At alltimes the contact member will make electrical connection with portionsof this resistance element within a plane perpendicular to the axis ofthe resistance element itself so as to obtain extremely great orinfinite resolution as indicated in the preceding discussion.

The various constructions of resistance elements and wipers hereindisclosed by reference are considered to be particularly applicable tounits such as accelerometers where it is desired to have a high degreeof resolution and where it is normally desired to use as small aresistance element as possible in order to avoid the necessity ofmechanical linkages and the like. Instruments of the present inventionhaving a high degree of resolution or infinite resolution are consideredto be extremely well adapted for such use. In addition the use ofcontact means having fingers capable of vibrating at different resonantfrequencies is considered to be extremely important in eliminatingcertain errors which frequently occur in the operation of electricalinstruments of the type to which this invention pertains.

Because of the fact that this invention is capable of exceedingly widemodification, it is to be considered as being limited only by theappended claims forming a part of this disclosure.

We claim:

1. An accelerometer which includes: a housing; means movable in responseto acceleration mounted within said housing; a wound resistance elementhaving a uniform cross-sectional configuration along its length mountedwithin said housing; and contact means mounted on said means movable inresponse to acceleration, said contact means engaging substantially allpoints of said resistance element in a plane perpendicular to the axisof said resistance element and being movable along the length of saidresistance element as said means movable in response to acceleration aremoved within said housing.

2. An accelerometer which includes: a housing; spring means positionedwithin said housing so as to be secured thereto; mass means attached tosaid spring means within said housing so as to be movable in response toacceleration; a wound resistance element having a uniform crosssectionalconfiguration along its length mounted within said housing; and contactmeans carried by said mass means, said contact means engagingsubstantially all points of said resistance element within a planeperpendicular to the axis of said resistance element, said contact meansbeing movable along the length of said resistance element duringmovement of said mass means.

3. An accelerometer which includes: a housing; first and second bellowsmeans mounted within said housing so as to define chambers within saidhousing; mass means secured to both of said bellows means so as toextend between said bellows means; contact means attached to said massmeans so as to extend therefrom; and a wound resistance element locatedwithin said housing so as to extend around said mass means and saidcontact means, said resistance element having a uniform cross sectionalconfiguration along its length and being engaged by said contact meansin substantially all points of said resistance element within a planeperpendicular to the axis of said resistance element, said contact meansbeing movable along the length of said resistance element duringmovement of said mass means so as to always engage substantially allpoints of said resistance element within a plane perpendicular to theaxis of said resistance element.

4. An accelerometer as defined in claim 3 including means defining adamping passage leading through said mass means and connecting saidchambers.

5. An accelerometer comprising a housing having a cavity providedtherein, a mass member disposed within said cavity, spring meansyieldingly supporting said mass member for linear movement in onedirection or the other responsive to acceleration forces, an elongatedresistance element of uniform cross section, and a contact elementengaging said resistance element at substantially all points thereonwithin a plane perpendicular to the longitudinal axis of said resistanceelement, one of said elements being mounted on said mass member andmovable therewith, and the other of said elements being mounted on saidhousing.

6. An accelerometer as defined in claim 5, wherein said elongatedresistance element is mounted on said housing parallel to the line oftravel of said mass member, and said contact element is mounted on saidmass member and movable therewith.

7. An accelerometer as defined in claim 5, wherein said housing isprovided with an aperture, said resistance element being attached to thesurface of said aperture around the circumference thereof, said massmember projecting through said aperture parallel to the longitudinalaxis thereof, and contact means on said mass member engaging saidresistance element around substantially the full circumference thereofwithin a plane perpendicular to the longitudinal axis of said aperture.

8. An accelerometer as defined in claim 5, wherein said resistanceelement is mounted on the surface of said housing within a cylindricalaperture therein, said cylindrical aperture being disposed with itslongitudinal axis parallel to the line of travel of said mass member,and said contact element being in the form of a ring mounted on saidmass member in a plane perpendicular to the longitudinal axis of saidcylindrical aperture.

9. An accelerometer comprising a housing having an enclosed cavityprovided therein, said cavity including two spaced apart end portionsjoined together by a cylindrical portion, a cylindrical mass memberextending through said cylindrical cavity portion concentric therewith,said mass member being supported at its ends by resilient springdiaphragms mounted within said end portions of said cavity, a restrictedpassage extending through said mass member from one end thereof to theother and connected to said end portions of said cavity beyond saiddiaphragms, said restricted passage providing an orifice damping effectas said mass member moves responsive to acceleration, a resistanceelement attached to said housing within said cylindrical cavity portion,and a contact member on said mass member engaging said contact member atsubstantially all points thereon within a plane perpendicular to thelongitudinal axis of said cylindrical cavity portion.

References Cited in the file of this patent UNITED STATES PATENTS686,245 Bachmann et al. Nov. 12, 1901 2,178,241 Rubinstein Oct. 13, 19392,570,672 Hathaway Oct. 9, 1951 2,886,676 Bourns et al. May 12, 1959

